Block copolymers having a styrene polymer block and a conjugated diene polymer block [hereinafter referred to as “styrene-conjugated diene block copolymer”] and the hydrogenated products thereof can be readily formulated into a molded article, because they can be plasticized and molten by heating. They have rubber elasticity at an ordinary temperature and show excellent balance between flexibility and mechanical characteristics. Therefore, in recent years, they have been widely used in various fields as one of the thermoplastic elastomers.
The styrene-conjugated diene block copolymers and the hydrogenated products thereof, which have low polarity, can be used in melt-adhesion or integral molding with a plastic of the same type having low polarity, but can be hardly melt-adhesive to a plastic having high polarity or a metal.
The British Patent No. 1581167 [GB 1581167] describes a composition in which a thermoplastic resin having specific properties is blended with a styrene-conjugated diene block copolymer and/or a hydrogenated product thereof. The publication discloses that the composition is suitable to insulators for conductors and soldering wires, and that a thermoplastic polyurethane is used as one of the thermoplastic resins described above. However, since the styrene-conjugated diene block copolymer, which may be hydrogenated, and the thermoplastic polyurethane is poor in compatibility, the properties of each polymer fail to be provided sufficiently, and a useful polymer composition cannot be obtained.
Further, various proposals have been made so far for the techniques with an aim of improving the melt-adhesiveness of the styrene-conjugated diene block copolymer or the hydrogenated product thereof. For example, a melt-adhesive composition comprising a styrene-conjugated diene block copolymer, which may be hydrogenated, and a thermoplastic polyurethane has been known [see the U.S. Pat. No. 5,472,782 and the Japanese Patent Application Laid-open No. Hei 8-72204]. However, this melt-adhesive composition sometimes results in a problem of failing to give a sufficient bonding strength or the lack of the durability of a bonding strength depending on the kind of the material laminated therewith. Moreover, the compatibility between the styrene-conjugated diene block copolymer, which may be hydrogenated, and the thermoplastic polyurethane in this melt-adhesive composition is not quite satisfactory, so that the composition has a problem such as delamination or instability of the bonding strength in the laminate structure obtained, for example, by composite injection molding.
Also, a polymer composition comprising a thermoplastic polyurethane and a styrene-conjugated diene block copolymer, which may be hydrogenated, modified with hydroxyl group, carboxyl group or a derivative thereof has been proposed with an aim of improving the compatibility between the styrene-conjugated diene block copolymer, which may be hydrogenated, and the thermoplastic polyurethane [see the U.S. Pat. No. 5,115,035 and the Japanese Patent Application Laid-open No. Hei 3-234755]. Further, there has been proposed addition of a phosphorus compound or a phenolic compound to the above-described composition to improve the thermal stability during processing [see the Japanese Patent Application Laid-Open No. Hei 7-126474]. However, a satisfactory result has not yet been obtained, because these compositions are still poor in non-tackiness, melt-moldability such as melt-retention stability, and melt-adhesiveness to other resins upon lamination.
As a polymer composition which can solve the above-described problems, the U.S. Pat. No. 6,106,952 discloses the polymer composition comprising (1) a block copolymer, which may be hydrogenated, of an aromatic vinyl compound and a conjugated diene, (2) a block copolymer having a polymer block (I) of a block copolymer, which may be hydrogenated, of an aromatic vinyl compound and a conjugated diene, and a polymer block (II) of a polyurethane, (3) a thermoplastic polyurethane and (4) a paraffin oil.